Sod slabs are harvested in a serial manner by a harvesting machine which removes them from the ground continuously. FIG. 1 generally illustrates a typical cutting head 100 used on harvesting machines. As shown, cutting head 100 employs two rollers: a leading compaction roller 101a which presses down on the turf to compact it before it is cut; and a ground reference roller 101b that sets the position of the cutting head with respect to the ground. Other harvesting machines will combine the two roller functions into the ground reference roller, or ignore the turf compacting function in general.
Cutting head 100 also includes a transverse chopping blade or blades 102a which chop the slab to length at the leading edge, which also forms the trailing edge of the preceding slab. Also, to separate the slab from the ground, cutting head 100 includes a cutting blade 102b that reciprocates in the longitudinal direction (i.e. the direction that the harvesting machine moves across the field (or left and right as shown)). Cutting blade 102b may have finger-like extensions 103 that trail behind the blade and lift the slab of turf grass up to the start of a conveyor 104 as the harvesting machine advances.
To produce a quality slab, cutting blade 102b must be positioned in such a manner as to maintain a reasonably uniform thickness of sod along the transverse length of the blade. As the ground where the grass is grown is not perfectly flat, it is important that the cutting head tip from side to side in order to follow the local undulations in the surface of the field. If the cutting head does not tip with the contour of the ground, the slab can have a non-uniform thickness. FIG. 2A illustrates an example of a slab 201 that has a non-uniform thickness across its width. Such variations in the slab thickness transverse to its length can produce tapered rolls which do not roll up properly, adversely affecting the quality of the turf.
Also, cutting blade 102b must be positioned in such a manner as to maintain a reasonably uniform thickness of sod along the longitudinal length of the slab. FIG. 2B illustrates an example of a slab 202 that has a non-uniform thickness along its length. Slabs that vary in thickness longitudinally when stacked produce a pallet that is tipped to one end and thus less stable. Additionally, severe variations in thickness result in slabs that may break apart when handled making the subsequent laying of slabs very difficult.
Conveyor 104 must be positioned with respect to cutting blade 102b so as to properly capture the slab of sod as it comes off of extensions 103. If conveyor 104 is too low it may drag on the ground behind the cut, whereas if it is too high, the slab may fall between conveyor 104 and extensions 103 back onto the ground.
It is also desirable for the cutting head and conveyor to lift high enough off of the ground that, when maneuvering or transporting the harvester, the conveyor and cutting head do not drag on the ground and to facilitate servicing of the cutting head.
Finally, the cutting head needs to be visible to the operator of the harvesting machine to not only initiate the cutting operation, but also to monitor the quality of the product going up the conveyor.
Current cutting head designs have various problems. For example, some cutting heads employ a simple spindle and bearing arrangement to move cutting blade 102b with the contour of the ground. The spindle and bearing arrangement typically pivots forward of the cutting head. Such cutting heads have a ground reference roller that is several inches aft of the spindle and produces a large vertical bending load on the spindle. This leads to a fracture failure of the spindle.
Some designers have attempted to mitigate this problem with a trailing roller that follows a cam track. Others have supported the trailing end of the cutting head with a multiple bar linkage. These designs are often inadequate because the cams and linkages are supported by structures that block the view of the operator.
Also, cam type supports lack strong transverse stiffness which is necessary to prevent some sideways skewing of cutting blade 102b. The support mechanisms used in cam type systems also wear quickly due to sand particle contamination leading to failure of the spindle if not regularly replaced. Additionally, spindle systems lack transverse stiffness. This results in transverse flexing of the cutting head that skews the blade trajectory with respect to the longitudinal direction of travel leaving an undesirable ragged edge on the slab.
Finally, in current designs, the conveyor can generally only be raised a few inches and thus gets damaged by obstacles during field maneuvering and transport. Also, to lift the conveyor, a separate conveyor lifting mechanism is often used. Because separate lifting mechanisms are used for the conveyor and the cutting head, the operator must coordinate the positions of the conveyor and cutting head. Further, if the cutting head and the conveyor are rigidly connected, it is difficult to lift the head high enough for easy service.